Pre-Lab Questions Flashcards
What is oiling out?
Oiling out is when a compound is insoluble in a solution at a temperature above the compound’s melting point. To prevent this, solvent should have lower BP than compound.
What procedural errors could reduce crystal amount?
- excessive washing in solvent 2. not allowing enough time to precipitate such that some acid still remains dissolved in solution 3. Not allowing the washed and recrystallized phthalic acid th dry sufficiently before removal, resultin in phthalic acid stuck on filter paper
If p-toluic acid were added to a two-layer mixture of TBME and water what would happen?
it would dissolve in the water because it is soluble in water
How does an increase in the heating rate change the temperature?
An increase in the heating rate does not change the temperature of the boiling liquid but instead increases the rate at which vapor is produced from the liquid
Extraction vs. Washing
Extraction: desired compound changes layers Washing: impurity changes layers
What is sublimation
When crystals vaporize without first turning into a liquid
Why is it important to prevent air bubbles from forming in the column bed (column chromatography)?
if air bubbles form, eluent will flow around the bubbles and large air bubbles may stop the eluent completely from flowing
What may result in error in MP analysis?
- use of coarse substance that results in air pockets that slow heat transfer 2. use of too much substance (>2mm) resulting in poor heat transfer 3. Heating too fast resulting in difference between temperature of thermometer and heat source
How do you isolate p-t-butyl phenol after extracting it into NaOH solution?
add HCl drops until acidic then cool in an ice bath and collect crystals over ice bath
What would happen if you added sodium p-toluate instead of p-toluic acid to the two layer mixture of TBME and water?
p-toluic acid would dissolve in water since its soluble in water
Why should you not add boiling chips to a boiling liquid?
Because the large surface area of the boiling chips can cause the hot liquid to foam out of the apparatus and cause burns
What happens if you add to much activated carbon?
it absorbs impurities and your compound. Results in lack of crystal formation
2 useful functions for MP?
- assessing purity 2. determining identity of unknown
What is the order of polarity of the compounds used in TLC? (benzhydrol, benzophenone, biphenyl)
Most to least polar 1. benzhydrol 2. benzophenone 3. biphenyl
